Wiki info about P-51D-5

The North-American P-51 Mustang was an American fighter designed in the early 1940s and is considered the best US fighter of WWII. It was widely exported to countries in Europe, Asia, Africa and South America. The P-51 participated in the Korean War and other post-WWII conflicts.
The most famous Mustang version was the P-51D with teardrop (or bubble) canopy. The main problem for the pilots of the earlier variants was a huge blind spot at the rear of the aircraft due to the canopy design. An earlier attempt to address the issue was a British-designed Malcolm hood, installed on many P-51Bs. It improved rearward visibility, but the search for a better solution continued. In January 1943, USAAF's Colonel Mark Bradley, while stationed in Britain, was introduced to the then-new "bubble" canopy, designed for use on Spitfires and Typhoons. The canopy had no framework and offered near 360-degree vision. To install the new canopy, the rear fuselage section of the Mustang had to lose some height. However, this change required minimal redesign to the airframe. The inaugural flight of the new P-51D took place at Inglewood, California on 17th November 1943.